For the purpose of improving fuel efficiency of an engine, a reduced cylinder operation may be performed in accordance with a driving state. Further, a homogeneous-charge compression ignition (HCCI) technology has been developed, in which self-ignition combustion is performed in a predetermined range in a gasoline engine. The fuel efficiency can be improved also by performing HCCI combustion.
However, when the reduced cylinder operation or the HCCI combustion is performed, the combustion of the engine tends to become unstable, and vibrations by torque fluctuation or the like tend to increase. The vibrations of the engine are transferred through a transmission and a differential device to a drive shaft that couples the differential device and a driving wheel. When the vibrations transferred to the drive shaft are transferred through a suspension arm and the like to a vehicle body, they become a cause of unpleasant vibrations and noise in a vehicle interior.
The vibrations transferred from the engine to the transmission can be absorbed by a torque converter. However, when the torque converter is in a lockup state or when a power train does not include the torque converter, the engine and the transmission are directly coupled to each other, so that the absorption of the vibrations by the torque converter cannot be realized. Therefore, when a lockup range is expanded for the improvement of the fuel efficiency or when the torque converter is omitted by, for example, realizing multistage of an automatic transmission, problems of the above vibrations and noise become more serious.
Examples of the vibrations of a power transfer system include vibrations caused by meshing of gears in the transmission or the differential device and torsional vibrations caused by impact at the time of torque inversion at a universal joint on the drive shaft, in addition to the above vibrations originated from the engine. When such vibrations are transferred through the drive shaft to the vehicle body, the same problems as above occur.
To suppress the above vibrations of the power transfer system, PTL 1 discloses a technology in which: a damper is arranged on a drive shaft that couples a differential device and a driving wheel; and the damper absorbs vibrations transferred from a power source constituted by an engine, a transmission, the differential device, and the like. Specifically, this damper is provided between a pair of universal joints arranged on the drive shaft and includes: a shaft portion provided at a tip end of a shaft extending from a power source-side universal joint out of the pair of universal joints toward the wheel; and a tubular portion provided at a tip end of a shaft extending from a wheel-side universal joint out of the pair of universal joints toward the power source. The shaft portion and the tubular portion are fitted to each other through an elastic member.